diff --git a/cortex/tests/test_utils.py b/cortex/tests/test_utils.py
index 65c1c813..22ee0c93 100644
--- a/cortex/tests/test_utils.py
+++ b/cortex/tests/test_utils.py
@@ -1,14 +1,76 @@
+import shutil
+import tarfile
+from unittest import mock
+
+import pytest
+
 import cortex
 
-def test_download_subject():
-    # Test that newly downloaded subjects are added to the current database.
 
-    # remove fsaverage from the list of available subjects if present.
-    if "fsaverage" in cortex.db.subjects:
-        cortex.db._subjects.pop("fsaverage")
+@pytest.fixture
+def fake_fsaverage_tarball(tmp_path):
+    """Build a minimal fsaverage.tar.gz that pycortex will recognize as a subject."""
+    subj_src = tmp_path / "src" / "fsaverage"
+    subj_src.mkdir(parents=True)
+    (subj_src / "marker").write_text("ok")
+    tarball = tmp_path / "fsaverage.tar.gz"
+    with tarfile.open(tarball, "w:gz") as tar:
+        tar.add(subj_src, arcname="fsaverage")
+    return tarball
+
+
+@pytest.fixture
+def isolated_filestore(tmp_path, monkeypatch):
+    """Redirect cortex.db.filestore to an empty tmp dir and reset the subject cache."""
+    store = tmp_path / "store"
+    store.mkdir()
+    monkeypatch.setattr(cortex.db, "filestore", str(store))
+    original_subjects = cortex.db._subjects
+    cortex.db._subjects = None
+    yield store
+    cortex.db._subjects = original_subjects
+
+
+def test_download_subject(isolated_filestore, fake_fsaverage_tarball, monkeypatch):
+    # Newly downloaded subjects are added to the current database.
+    def fake_retrieve(url, dest):
+        shutil.copy(fake_fsaverage_tarball, dest)
+        return dest, None
+
+    mock_retrieve = mock.Mock(side_effect=fake_retrieve)
+    monkeypatch.setattr(cortex.utils.urllib.request, "urlretrieve", mock_retrieve)
 
     assert "fsaverage" not in cortex.db.subjects
     cortex.utils.download_subject(subject_id='fsaverage')
     assert "fsaverage" in cortex.db.subjects
-    # test that downloading it again works
+    assert mock_retrieve.call_count == 1
+
+
+def test_download_subject_skips_when_present(isolated_filestore, monkeypatch):
+    # If the subject is already in the database and download_again is False,
+    # download_subject warns and returns without touching the network.
+    cortex.db._subjects = {"fsaverage": mock.MagicMock()}
+
+    mock_retrieve = mock.Mock()
+    monkeypatch.setattr(cortex.utils.urllib.request, "urlretrieve", mock_retrieve)
+
+    with pytest.warns(UserWarning, match="already present"):
+        cortex.utils.download_subject(subject_id='fsaverage')
+    mock_retrieve.assert_not_called()
+
+
+def test_download_subject_download_again(
+    isolated_filestore, fake_fsaverage_tarball, monkeypatch
+):
+    # download_again=True re-downloads even when the subject is already present.
+    def fake_retrieve(url, dest):
+        shutil.copy(fake_fsaverage_tarball, dest)
+        return dest, None
+
+    mock_retrieve = mock.Mock(side_effect=fake_retrieve)
+    monkeypatch.setattr(cortex.utils.urllib.request, "urlretrieve", mock_retrieve)
+
+    cortex.utils.download_subject(subject_id='fsaverage')
+    assert "fsaverage" in cortex.db.subjects
     cortex.utils.download_subject(subject_id='fsaverage', download_again=True)
+    assert mock_retrieve.call_count == 2